Paper machinery



F. B. K. GREEN PAPER MACHINERY Dec. 6, 1960 3 Sheets-Sheet 1 Filed Sept.22, 1955 F. B. K. GREEN Dec. 6, 1960 PAPER MACHINERY 3 Sheets-Sheet 2Filed Sept. 22, 1955 lIrIrI/I Fig. 5.

n m m m BY FRANK B. K .GREEN 7 ,44 w4 ATTORNEYS Dec. 6, 1960 F. B. K.GREEN 2,963,086

PAPER MACHINERY Filed Sept. 22, 1955 3 Sheets-Sheet 3 l five/#0! 45 UFrank B. K.Green 53 4 B,MMM

PAPER MACHINERY Frank B. K. Green, Massapequa, N.Y., assignor to Pandia,

Inc., New York, N.Y., a corporation of New York This invention relatesto the digestion of lignocellulosic fibrous, material for rendering theligneous and other fiberencrusting contaminants amenable to removal sothat cellulosic fibers canbe obtained in a form that lends itself tomaking them into paper, paperboard, nine point and related products;

Such fibrous material as wood-chips, for instance, is digested or cookedin chemical liquor capable of rendering the ligneous constituentswater-soluble. The cooking is done in digesters while under heat andpressure with the wood-chips submerged in the digestant liquor. Thedigesters are filled and emptied periodically on a batch basis. Effortshave been made to carry-out such digestion on a continuous basis, andone process and apparatus that has proven successful is shown in theBeveridge and Kehoe Patent No. 2,422,522 issued June 17, 1947, andassigned to the assignee of this application. The inven- United StatesPatent tions of thatpatent proposed that the wood-chips be forcibly fedto a heat-and-pressure conduit-like flowpath embodied in a plurality ofsuperposed substantially horizontal tubes or pipes with a verticalconnection therebetween. In each pipe was a screw conveyor forprogressing the chips along the pipe in a controlled and uniform mannerwhile in non-submergence but subject to digestive or cooking treatmentin a gaseous environment from which the chips were discharged afterbeing defibrated while hot and under pressure. In that digestingapparatus, and in its normal operation, the horizontal pipes were rarelyfilled with chips being treated to an elevation higher thanthe axis ofthe pipe, so it is -a major object of this invention to devise ways andmeans, whereby those pipes can be substantially filled with chips beingtreated, and thereby to increase the effective capacity of thatapparams.-

However, certain kinds of pulp having a relatively high cellulosiccontent as compared with the residual ligneous content (called low-yieldpulps) heretofore have been made usually in batch digesters where thechips are maintained constantly in' submergence in the cooking liquor.In batch digesters penetration of the chips by the I cooking liquor isretarded by the packed condition of the chips in their relatively fixedposition while liquor is circulated over them, so another object of thisinvention is move the chips repeatedly and continually with respect toeach other as well as to the cooking liquor.

An additional object is to move the chips through a digester fromsubmergence to emergence and return so that they are exposed during thedigestion periodto submergence in the cooking liquor and to emergence inthe chemical-bearing gaseous atmosphere above the liquidlevel of theliquor. And a corollary to this object is to be able to exercise controlof the frequency and duration of the alternate submergence andemergence,

Still another object is to devise ways and means for carrying out thesubmergence and emergence of the chips while in a continuous digesterembodying a succession of substantiallyhorizontal material-supportingpipes or tubes while avoiding harmful cascading of the chips and withoutthe use of liquor-damming devices as such. 7

A still further object is to render some of the ligneousfiber-encrusting contaminants water-soluble but not actuallysimultaneously dissolved by having the liquor act on the chips whilenon-submerged, that is, emerged. The cooking liquors purpose is to reactwith these encrustations to render them water-soluble, but when thechips are cooking in submergence, as rapidly as the encrustants arerendered soluble, they are dissolved; so by the practice of thisinvention, some of the encrustants, while in emergence, are renderedsoluble and thereafter they are dissolved when submerged, whereas othersof the encrustants, while in submergence, are both rendered soluble andconcurrently dissolved.

Reference is also made to Kehoe et al. Patent No.

2,616,802, issued November 2, 1952 to the assignee of this application,which discloses a method and applications whereby steam-softened chipsare fragmentized while in a mobilized turbulent mass thereof in gaseoussuspension followed by a final sizing of these fragments by projectingthem threadingly through a size-controlling orifice. In order to dothis, the steam-softened chips must not be in submergence, so it isanother object of the present invention to devise ways and means forcombining this type of fragmentizing and size-controlling discharge withdigestion treatment of the chips by the alternate liquor submergence andemergence thereof that is one of the objects of this invention.

Additional objects and advantages will be apparent from the followingdescription, the accompanying drawings and the appended claims.

In the drawings:

Fig. 1 is a view partly in side elevation and partly broken away invertical section showing continuous digesting apparatus constructed inaccordance with the invention;

Figs. 2, 3 and 4 are somewhat diagrammatic cross-seetional views takenon the lines 2-2, 33 and 44 respectively of Fig. 1; I

Fig. 5 is an enlarged and somewhat diagrammatic fragilar to that of Fig.1 but incorporating additional digesting tubes.

In the embodiment of the invention shown in the drawings, andparticularly Fig. 1, there is a feed hopper 11 to which chips, or otherligno-cellulosic material to be treated, are supplied. Chips are forcedfrom the bottom of the hopper by a motivated feed-screw feeding means12, through a feeding-in section A comprising a pipe 13 of progressivelydecreasing diameter connected to an intermediate pipe 14 of uniformdiameter which in turn is connected to another pipe 15 of enlargingdiameter leading to a T-piece 16. Steam is delivered to the feedinginsection as by valved pipe 17, and liquor is delivered to the feeding-insection as by the valved pipe 18, so that it is sprayed into the T-piece16. In the drawings, the parts included in the A bracket comprise thefeedingin section while the parts included in the B bracket are oftencalled collectively the pre-heater.

The vertical T-piece 16, down which chips have freefall, leads to a pipeor tube 20 which is sufiiciently horizontal to be material-supporting;that is, chips remainin it by gravity. This tube has within it a drivenscrew conveyor 21 with usual screw flights 22 on a central shaft 23supported from the closure ends 24 and 25 of the tube adjacent theclosure end and carried by the shaft 23 is a conical deflector disk 26,coned toward the length of the tube 20, to keep the chips away from thebearing of the shaft 23, and a similar coned deflector disk 27, butoppositely directed, is carried by the shaft 23 adjacent the otherclosure end 25 of the pipe. At the end of the tube 20 opposite its inletfrom the T-piece 16 is an outlet connection 30 sufliciently vertical sothat chips have freefall therethrough. Projecting into the mouth of thefreefall connection 30 is an open-ended shelf-like plate 28, havingperforations 29 therein, which form a strainer means for a purposehereinafter described.

The free-fall connection 30, while comprising the discharge outlet fromthe tube 20, also comprises the feedinlet to a subjacent tube 31 whichis in all respects similar to the tube 20, except that it can beoppositely directed as shown. It has one closure. end 35, and anopposite closure end 36, in which are rotatably supported a screwconveyor 37 having a shaft 38 and screw flights 39. At the right-handend of the tube 31 there is a deflector disk 41 like deflector disk 26of pipe 20 and for the same purpose, but the deflector disk 42 whichcorresponds to deflector disk 27 in tube 20 differs in that it hasperforations 43 (Fig. for liquor-drainage purposes. And also fordrainage purposes, the first few screw flights (at the left) on conveyor37 in pipe 31, adjacent the draining deflector disk 42, haveperforations 44. In the left-hand closure end 35 of tube 31 is adrainage pipe 45, valved at 46.

In Figs. 1 and 10, the strainer disks 42 are shown carried by the shaft38 of the screw conveyor, but under certain circumstances it isadvantageous to have the strainer disk fixed, as shown at 42' in Fig. 9.Here the disk 42' with its perforations 43' is fixed to the periphery ofthe bore of the tube 31, as at 47. At the apex, the

disk 42' has a hole or bore 48 through which shaft passes with ampleclearance so as not to bind.

The tube 31 has a free-fall outlet connection 50 at its opposite endwhich may lead to another materialsupporting tube with a screw conveyorin it, constructed generally like tube 31, and this arrangement ofvertically spaced tubes connected by free-fall connections can bemultiplied so that there are as many as four (see Fig. 11) or more suchtubes. However, for simplicity purposes, only two are shown.

The lowermost tube discharges through its free-fall connection 50 into achip-fragmentizing discharge section indicated generally by the linesleading to the letter D. This fragmentizing discharge section is shownand described in the previously mentioned patent of Kehoe, et al., No.2,616,802. In essence, it comprises a closedbottomed chamber 51 intowhich steam-softened chips fall where they encounter an intenselyrapidly moving bladed impeller 52 whose rapidity of motion renders thesoftened chips into a highly turbulent, mobilized mass in substantiallygaseous suspension, such that there results an initial fragmentation ofthe chips. These fragments are then projected through a particle-sizecontrolling orifice 53, partly by the force of the impeller and partlyby the stream of steam issuing therethrough. The size of the orifice iscontrolled by regulating devices 54 and the final fragmentized particlesare discharged to the atmosphere through pipe 55. Pipe 56 is merely forclean-out purposes. In this, and the other figures, the chips areindicated collectively and separately by the letter C, the liquor in thepipes, hereinafter to be described, or perhaps rather the liquid-levelthereof, by the letter L, and the steam or other atmosphere over theliquor, by the letter G.

Since a main feature of this invention is to treat the chips toalternate submergence in digesting liquor and emergence therefrom, suchliquor is pondingly held in pipe 20 with a liquid-level about as shownin Fig. 1, wherein it is fairly level at the right-hand end or feed-inend; but at the outlet or left-hand end, the liquid-level follows moreor less a parabolic curve. Figs. 2, 3 and 4 are cross-sectional views soin each the relation of liquid to superposed gaseous environment can beseen. At the inlet end of the tube, it is desired that the liquid-levelof the liquor be above the level of the shaft 23, whereas at theleft-hand end, it is to be below it, and this rela-. tionship changesprogressively as the outlet end of the tube is reached. This result isdue apparently to the fact that while the liquor in the pipe 20 forms ineffect one general pool or pond, actually it is divided into asuccession of individualized or component pools or ponds, with each poolbeing held between two adjacent screw flights, so one is separated fromits next-door neighbor; by a rotating substantially vertical flight. Theflights have a limited clearance from the inner periphery of the pipe20, as can be seen in Fig. 8, but with the chips compacted between theflights, due to their turning, there is a certain flow-retarding effectset up by them which prevents too much flow of liquor past the bottom ofthe flights. Some takes place but not much, so the liquidlevel graduallydecreases as can be seen from Figs. 2, 3 and 4. Of course, at the outletend of pipe 20, the liquid-level goes to nothing as shown because of theflow of liquor over and down from the bottom edge of the pipe 20 throughthe free-fall connection 30. Thus, at the inlet end of the tube, eachhydraulically connected compartment made between two adjacent flightshas more liquor in it than gas, and at the outlet end, each compartmenthas in its more gas than liquor.

In order to obtain maximum through-put for the apparatus, it isimportant 'to assure that evenv when the pipe is filled to maximumcapacity with chips, the chips will advance through the pipe at theproper rate with minimum tendency toward rotation with the conveyorscrew in such manner as to cause plugging of the pipe, and the presentinvention accomplishes this desired result. Referring to Fig. 7, withthe screw rotating clockwise as shown, the efiect'of the screw incooperation with the forces of gravity is to cause compaction of thechips into an area X represented by the double cross hatching. Thesloping top or inner surface of the area X remains fairly constant atall loadings of the tube at or above the lowest operating conditions forwhich the unit is designed providing that proper advance of the chipsaxially of the tube is maintained, and the outer surface of area X isshown as extending circumferentially of the tube from a positionbelowits horizontal center line on the downwardly moving side of thescrew to a position above the horizontal center line on the upwardlymoving side of the screw.

The plugging tendency of the chips referred to above appears to dependupon the frictional relation between the chips on the one hand and boththe inner surface of the tube casing and the flights of the conveyorscrew. When the unit is less than half full, the weight of the chipsbetween the screw flights is supported by the casing, and the frictionbetween the chips and the inner surface of the casing is suflicientlygreater than the friction between the chips and the screw flights thatthe chips will not turn with the flights but will advance axially of thetube as the flights pass through them. However. such loading conditionsresult in a low capacity throughput for the apparatus, and when thecapacity is increased by filling the tube to any level above the top ofthe screw shaft, two other forces come into play which upset thefriction balance in the unit in favor of the rotating screw.

The first of these additional forces is illustrated in the diagram inFig. 8. The chips lying directly above the screw shaft 23 andrepresented by the double crosshatched area Q are supportedsubstantially directly by weight of the chips supported by the wall ofthe casing does not increase in direct proportion to the total weight ofthe chips present in the tube when the chip level rises above thehorizontal centerline of the tube.

The second additional force derives from the fact that while the chipsresting on the bottom of the tube directly on its vertical center lineare supported by the tube wall, as the helix of the screw flightdevelops in the direction of rotation and the chips increase in depth,the weight of the chips supported by the flight increase because of theinclining face of the flight inherently present. This additional weightalso favors the rotating force, which increases to a greater extentproportionately upon increased loading than does the weight supported bythe casing.

To recapitulate: when the tube is less than half full, almost all of theweight of the chips is supported by the tube casing, and the frictionbalance favors the casing. When the chips fill the tube above the top ofthe screw shaft, then the shaft and the screw flight supports the weightof some of the chips, thus proportionately reducing the load which issupported by the casing. This weight supported by the screw is alsosubjected to rotation of the screw, and this apparently creates enoughtotal friction to cause the chips to rotate as a mass with the screwrather than to advance through the tube, thus effectively plugging thetube.

In accordance with the present invention, it has been determined thatthe proper frictional conditions for maintained axial advance of thechips under conditions of high loading, as well as for the desiredrotational movement of the chips for repeated submergence in thedigesting liquor and emergence therefrom, are established by theprovision of a plurality of spline bars extending lengthwise of the tubeand projecting inwardly from the inner surface of the tube casing withinthe area X. Since the top surface of the area X remains essentiallyconstant as previously noted, the center of this area remains similarlyconstant and appears to be located below center and approximately midwaybetween the vertical and horizontal center lines of the tube on theupwardly moving side of the screw. For this reason, one spline bar 61 isdesirably located at this 45 position as shown in Fig. 6. A secondspline bar 62 should be located above spline 61 within the area X, andthe position ofthis spline on the horizontal center line as shown inFig. 6 has been found to give the desired results in operation byoflering' additional resistance to rotation of the chips with the screw.

When the level of the chips in the tube rises above the screw shaft 23,the uppermost chips tend to be conveyed over to the downwardly movingside of the screw, particularly those chips lying in the areacorrespondingly to the area Q in Fig. 8, and these chips fill the single.cross hatched area Z in Fig. 6. The position on the inner wall of thetube casing where the areas X and Z meet appears to remain practicallyconstant, and it also appears that when the level of chips in the tubereaches the point at which the chips begin to travel over the top of thescrew shaft, the forces in the area X are at a maximum. If, therefore, athird spline bar 63 is located at the lower junction of the areas X andZ, further increase in the chip level will not alter the forces in thearea X. The proper location for the spline 63 appears to be between thevertical center line and the adjacent 45 position on the downwardlymoving side of the screw, with preferred results having been obtainedwith this spline 22.5 from the vertical as shown in Fig. 6. The splines6163 should run substantially the entire length of the tube, and thecompacting or compreming action of the rotating screw in combinationwith the resisting or retarding action of the splines aids in thedisintegration of the chips in a long cook. r j

The pattern assumed by the chips in the tube as described in connectionwith Fig. 6 is of special importance at the position immediately belowthe inlet to the uppermost tube 20 because of its relation to the freshmaterial being supplied to the tube from the inlet. Referring to Fig. 7,since the chips assume the sloping pattern in the area X for the reasonsdescribed, if the fresh chips fall on to the upwardly moving side of thescrew, they tend to stay in such position. As a result, those of thesechips lying above the liquor level at the inlet end of the tube may notbe submerged in liquor for a considerable time, especially if the unitis running at low capacity. 6

In contrast to the condition just described, if the fresh chips fallonto the downwardly moving side of the screw, they are receivedinitially in an area of minimum chip concentration and maximum liquorlevel, so that at least the majority of the fresh supply of chips willbe caused to pass through a pond of liquor before reaching the area X.As shown in Fig. 7, this desired result is accomplished by providing inthe inlet connection 16 an inclined baflle 66 arranged to direct theincoming chips to fall tangentially into the tube 20 on the downwardlymoving side of theconveyor screw. This arrangement is especiallydesirable when theunit is running'at high capacity, since it assuresimmediate submergence in liquor of the maximum amount of fresh chips,and thereafter all the chips will rotate slowly with the screw as theyprogress axially through the tube for thorough submergence in thedigesting liquor.

A somewhat different directional problem exists at the free-fallconnection from each tube to the next lower tube, which is illustratedfor tubes 20 and 31 in Fig. 10. Since the connection 30 leads at rightangles into the tube 31 similarly to a T piece, if the chipsare free tofall directly through the connection 30 as soon as they reach it, theytend to pile up in pipe 31, and then as the flights of the conveyorscrew bite into this pile, undesirable shearing of the chips can takeplace between the flights and the lower edge of the connection 30. Thisresult isprevented in accordance with the invention by the provision ofthe plate 28, which acts as a deflector to direct the chips toward thefar side of the connection 30 as shown in Fig. 8.

With this arrangement including a deflector as shown at 28, the chipsfalling through the connection 30 have time in which to flatten out andrearrange themselves before they can be carried by the screw flights tothe junction between the connection 30 and the pipe 31, and -shearing ofthe chips at this junction is thus prevented. With the plate 28perforated as shown, the liquor earn drain through-the perforations 29for temporary segregation from the chips as both fall into the pipe 31,and-the liquor thus will spray over the chips as they have beenrearranged in the lower tube. In addition, the use of this deflectorplate 28 results in increasing the effective length of each tube andhence increases the cooking time for the same size and operating speedof the unit. In other words, the deflector plate adds its own axiallength to the distance the chips'must travel both in the tube in whichthe deflector plate is mounted and also in the adjacent lower tube.

It is desirable under certain conditions to have a minimum amount ofliquor in the final tube. This is'particularly true when thefragmentizing type of discharger D is to be used, for there the chipshave to be fragmentized in gaseous suspension so they should have aminimum of liquor with them. To the end of de-watering the chips, it ispossible to drain or suck oi? the liquor from the chips by the meansshown in Fig. 10. That is, the deflector disk 42 is perforated and soare the first few end flights of the screw, which permits the liquor tobe sucked out from that end of the tube 31 through the conduit 45 whichis to be connected to a pump, if desired.

Fig. 11 shows how the liquor can be drawn off throu h conduit 45 fromthe left-hand end of the bottom tube and also from the right-hand end ofthe adiacent upper tube, through connecting conduit 70. In the eventthat it is desired to recirculate some of the liquor, this can be donefrom the left-hand end of the second tube in Fig. 11 to the T-piece 16,by means of conduit 71 and its pump 72. Since the liquor can be heldback and ponded as described herein, more liquor can thus be added andused.

Operation Chips or other ligno-cellulosic material to be treated aresupplied to the feeding-in section A, namely to the hopper 11, fromwhence screw feeder 12 forced the chips into the preheater B, whilecompacting the chips into the form of plugs which plug the intermediatepipe 14 for minimizing escape past the plug of the heat and pressurewithin the flow-path housed by the conduit comprising the digestingtubes 20 and 31 with their free-fall connections 16, 30 and 50. The plugtends to expand as it enters the pipe 15 with its increased diameter,especially as it encounters there saturated steam supplied through pipe17. By the time the chips reach the T-piece 16, they have becomesubstantially disintegrated from their plug form, so that they are ineffect individualized again. It is important to get a proper concept ofthe relative sizes of the chips and the horizontal tubes such as 20. Thetubes may be 24 inches in diameter and in some cases are as large as 36inches. On the other hand, a wood chip ranges from the size of a silverhalf-dollar to a dollar although somewhat thicker at times, and the sizeof the chips is roughly indicated in the drawings by the small wavylines. They are compressed clingingly into a mass, but rather thancontinue the showing of the massed chips, broad crosshatching has beenused instead so as not to obscure the liquid-level of the ponded liquorin the pipes.

In falling down the T-piece 16, the chips are subjected to a spray ofstrong digesting liquor which comes in through the pipe 18. The chipsthen fall into the inlet end (right-hand end) of tube 20 in a tangentialmanner with respect to the screw conveyor flights 22, as shown in Fig.7, whereupon they begin their passage along the tube 20. Their transitof tube 20 is accurately controlled to be uniform and as to total timeby the speed of rotation of the screw conveyor 21. The quantity ofliquor supplied through pipe 18 is controlled to give the desired amountof liquor flowing through tube 20 to present a liquid-level L about asshown in Fig. 1. Due to the splines inwardly projecting from the innerperiphery of the tube 20, the chips in the tube do not rotate unitarilywith the screw conveyor as they would tend to do if the splines wereabsent but are submerged in the liquor pool and then caused to emergeinto the gaseous steam-bearing atmosphere overlying the liquor.

The liquor-level progressively decreases as the left-hand end of thetube is reached, as shown in Fig. l, and more particularly in Figs. 2, 3and 4. Thus near the righthand or inlet end of tube 20 more of the chipsare submerged in liquor than are exposed in the overlying gaseousatmosphere, whereas at the left-hand end, the reverse iS true, and thetransition from right-hand end to left-hand end, is progressive from onerelationship to the other. The splines assure alternate squeezedsubmergence and unsqueezed emergence of the chips in the tube so that itis not possible for some chips to remain in submergence while othersremain in the gaseous atmosphere.

An important function of the splines 61-63 is to increase the frictionbetween the inner periphery of the tube and the chips. The splines causethis increase in friction to a degree such as to overbalance thefriction between the chips and the screw flights for inducing squeezing,compression or compaction of chips between themselves so that theirtendency to lifting by the flights is retarded, and the chips arerearranged compressively in their mutual contact with each other. Thesplines help chips have time to flatten out and rearrange themselves sothat no pile of them develops in the inlet end of tube 31, whereupon thescrew conveyor 37 of that tube can pick them up and advance them to thefree-fall connection 50, either to another lower tube, like 20 or 31 butfinally to the fragmentizing zone D. In the latter, the steam-softeneddigested and dewatered chips are initially fragmentized in the chamber51 due to the action of the bladed impeller 52 which renders them into aturbulent mobilized gaseous suspension, from whence they are dischargedthrough an orifice 53 to pipe 55 and thus sized as to the diameterallfragmentation being along the lines of natural cleavage of the chips.

In a satisfactory embodiment, the digesting tubes were 35 inches ininside diameter, and the screw conveyor had a pitch of 12 inches with adiameter of 33 inches and was rotated at a speed ranging from 1 to 2rpm. The splines 61-63 were inch square so there was a clearance of inchbetween them and the screw flights. Center to center distance betweenfree-fall connections was 21 feet. The quantity of digestant liquor wasfrom 3 to 4 parts liquor to 1 part of wood chips. It was found possibleto hold liquor flowing through the pipe at any depth desired and thiswas governed solely by the rate at which the liquor was fed. Enoughsteam was used to maintain in the entire treatment conduit a temperatureof from 212 F. up to 375 F. and a superpressure appropriate to thetemperature to prevent boiling. Wood chips vary in diameter from aboutto inch. The digestant liquor maybe a solution of caustic soda in aconcentration of from 4% to 15%. And solutions of other chemicals usableare sodium sulfite, sodium carbonate, and the like.

Features of advantage of this invention include the submerging ofcompression-induced contacting chips in digestant liquor followed byemergence in the steam-bearing atmosphere above the liquor while not socompressed. One effect of this is that after the chips are covered withand somewhat penetrated by the'liquor, they are raised out of it intothe super-pressure super-temperature steam atmosphere where air is thusremoved from the chips so that when they are again submerged, moreliquor can penetrate the chips to do its work of removing the ligneousencrustations on the cellulosic fibers. The progress of the chips alongthe digesting tubes is carefully controlled by the screw conveyor andtheir spiralized motion from submergence to emergence is also carefullycontrolled by the splines projecting inwardly from the inner wall of thetubes. Then the relative position of the chips is repeatedly changed andrearranged in each compartment between adjacent flights by the expedientof the splines and by the expedient of the free-fall of the chips downthe free-fall connections from tube to tube, and at the same time therearrangement of the liquor is also assured by the segregation of theliquor from the chips during this free-fall by means of the strainingperforated plate means at the exit end of the tubes.

Further assurances of the control of the chips is given by thesubdividing of the pool of liquor into component pools each with its ownsuperposed gaseous atmosphere.

The component pools are horizontally separated by the rotating verticalscrew conveyor flights but the component pools are retained inperipheral hydraulic connection due to the permeable seal of chips inthe flow passages between the splines and the inner wall of the tube andpast the conveyor flights. This arrangement gives downstream flowofliquor from an upstream component pool to its next downstream neighborbut without letting too much liquor escape past the flight-to drain thepool of its liquor. In this manner the liquor is maintained in the tubewithout the use of dams per se. The liquid-level of the liquor ismaintained in the tube so that it is higher in the inlet end of the tubeand lower in the exit end of the tube, with the liquid-level assumingthe shape more or less like that of a parabolic curve. This is helpfulbecause the chips get the greatest depth of submergence at the inlet endof the tube and the greatest extent of gaseous atmosphere at the exitend.

This progressive transition from relatively great submergence torelatively great emergence seems to be very advantageous. The tangentialfeed of chips from the first free-fall connection into the uppermosttube seems to facilitate the spiralizing of the chips in the latter, for

otherwise there is a definite disturbance of forward flow of the chips.The liquor draw-0E straining means provided at the end of some tubes isof advantage in removing excess liquor from the chips before they go tothe fragmentizing discharger wherein they must be fragmentized in agaseous environment preparatory to being discharged through thesize-controlling discharge orifice. And, of course, by maintaining thehorizontal digesting tubes substantially full of chips at all times, thethrough-put or treatment capacity of such a digester is maximized overthose of a similar type wherein the tubes are maintained only partiallyfilled with chips.

This application is a continuation-in-part of'my application Serial No.420,033, filed March 31, 1954 as a continuation-in-part of myapplication Serial No. 261,278,

filed December 12, 1951, both of which prior applications are nowabandoned.

While the methods and forms of apparatus herein described constitutepreferred embodiments of the invention, it is to be understood that theinvention is not limited to these precise methods and forms ofapparatus, and that changes may be made therein without departing fromthe scope of the invention which is defined in the appended claims.

What is claimed is:

1. In continuous digesting apparatus of the character described forcellulosic material, comprising a pair of vertically spaced generallyhorizontally extending tubes each having an inlet in the top thereof andan outlet in the bottom thereof spaced axially from said inlet, meanssupporting said tubes with said inlet of the lower said tube verticallyaligned with said outlet of the upper said tube, a connection extendingvertically from said upper tube outlet to said lower tube inlet, meansfor introduc ing said cellulosic material into said upper tube throughsaid inlet, and means for supplying digesting liquor to said upper tubefor movement therethrough with said cellulosic material, the combinationof a conveyor screw extending lengthwise of each said tube, means forrotating each said screw in the direction to advance said cellulosicmaterial lengthwise of said tubes to said outlets thereof for free falltherethrough, and the improvement comprising a bafile mounted in fixedposition at the upper end of said connection and extending across aportion thereof nearest said inlet of said upper tube for directing saidfree falling material toward the portion of said connection furthestfrom said outlet of said lower tube to shearing of said material betweensaid aeeaose vertically spaced generally horizontally extending tubeseach having an inlet in the top of one end thereof and an outlet in thebottom of the opposite end thereof, means supporting said tubes withsaid inlet of the lower said tube vertically aligned with said outlet ofthe upper said tube, a connection extending vertically from said uppertube outlet to said lower tube inlet, means for introducing saidcellulosic material into said upper tube through said inlet, and meansfor supplying digesting liquor to said upper tube for movementtherethrough with said cellulosic material, the combination of aconveyor screw extending lengthwise of each said tube, means forrotating each said screw in the direction to advance said cellulosicmaterial lengthwise of said tubes to said outlets thereof while tendingin cooperation with gravity to compact said material in each said tubein an area extending from a position between the horizontal and verticalcenter lines of said tube on the downwardly moving side of said screwtherein to a position between said horizontal and vertical center lineson the upwardly moving side of said screw, spline bars within said areaof each said tube and secured to the inner surface of said tube forcooperation with said screws to resist the tendency of the compactedcellulosic material toward rotation with said screws and thereby tocause axial advance of said vmaterial to the adjacent said outlet forfree fall therethrough and to provide an area of minimum compaction ofsaid material including and below said horizontal center line on thedownwardly moving side of said screw, the improvement comprising meansin said inlet of said upper tube for directing said material introducedtherethrough toward the downwardly moving side of said upper screw andaway from the upwardly moving side thereof to effect delivery'of saidmaterial initially into said area of minimum compaction, and meanscovering a portion of the upper end of said connection nearest saidinlet of said upper tube for directing said free falling material towardthe portion of said connection furthest from said outlet of said lowertube to minimize shearing of said material between said screw in saidlower tube and the lower end of said connection.

3. In continuous digesting apparatus of the character described forcellulosic material, comprising a pair of vertically spaced generallyhorizontally extending tubes each having an inlet in the top thereof andan outlet in the bottom thereof spaced axially from said inlet, meanssupporting said tubes with said inlet of the lower said tube verticallyaligned with said outlet of the upper said tube, a connection extendingvertically from said upper tube outlet to said lower tube inlet, meansfor introducing said cellulosic material into said upper tube throughsaid inlet, and means for supplying digesting liquor to said upper tubefor movement therethrough with said cellulosic material, the combinationof a conveyor screw extending lengthwise of each said tube, means forrotating each said screw in the direction to advance said cellulosicmaterial lengthwise of said tubes to said outlets thereof'for free falltherethrough, the improvement comtially vertical perforationstherethrough to cause said liquor to drain therethrough onto saidmaterial in said lower tube.

(ltdereneuonlollowlngw) 11 References Cited in the file of this patentUNITED STATES PATENTS Pierce Mar. 10, 1896 Spurrier Sept. 12, 1899 5Conway Feb. 18, 1908 Day Sept. 30, 1924 Tarbox Jam 4, 1927 Sierer Feb.24, 1931 m Wollenberg June 27, 1933 Asplund Feb. 7, 1939 12 Merrill May7, 1940 Beveridge et a1. June 29, 1943 Ronning May 27, 1947 Beveridge eta]. Aug. 5, 1947 Kehoe et al. Nov. 4, 1952 Messing Dec. 22, 1953 SeglMar. 30, 1954 FOREIGN PATENTS Australia Aug. 28, 1940 Canada Apr. 3,1951 Sweden Nov. 13, 1934

